1. Field of the Invention
The present invention relates to a photovoltaic device, such as a solar cell assembly or a photosensor assembly, comprising amorphous semiconductor layers, wherein a plurality of power generation regions formed over one side of a substrate are arranged and connected in series, and a method of producing the photovoltaic device.
2. Prior Art
FIG. 4 is a cross-sectional view illustrating a construction of a conventional photovoltaic device in which power generation regions are connected in series. Referring to FIG. 4, numeral 21 designates an insulative substrate, numerals 22a and 22b designate the first electrodes (hereafter referred to as lower electrodes) coated over the substrate 21, numerals 23a and 23b designate amorphous semiconductor layers coated over the lower electrodes 22a and 22b respectively, and numerals 24a and 24b designate the second electrodes (hereafter referred to as upper electrodes) coated over the amorphous semiconductor layers 23a and 23b respectively. The insulative substrate 21 is a glass substrate which allows visible light to pass through, or a ceramic substrate. Among the lower and upper electrodes (22a, 22b, 24a, and 24b), those on the light incidence side are made of transparent tin oxide or indium oxide, and those on the other side are made of a nontransparent metal, such as aluminum, chromium or nickel.
The amorphous semiconductor layers 23a and 23b, which generate electrons when illuminated, have a construction of three layers (only one layer is shown in FIG. 4) comprising from the substrate a P-type layer, an i-type (non-doped) layer, and an N-type layer. The photovoltaic device described above has disadvantages, in particular in the method of production thereof. This method uses a metallic mask (not shown) having lower-electrode-shaped holes depending on the shape of the power generation regions (a', b' . . . ).
First, the mask is placed on the insulative substrate 21 and the lower electrodes 22a and 22b are coated over the insulative substrate 21 using a lower electrode forming unit. Then, the mask is moved by a specified distance in the arrangement direction of the lower electrodes 22a and 22b to cover the lower electrodes 22a and 22b with the mask. The amorphous semiconductor layers 23a and 23b are coated over the lower electrodes 22a and 22b using a plasma CVD unit. The mask is further moved by said specified distance in the same direction onto the amorphous semiconductor layers 23a and 23b. Then, the upper electrodes 24a and 24b are coated over the amorphous semiconductor layers 23a and 23b using an upper electrode forming unit.
As a result, the conventional photovoltaic device in which the upper electrode 24a of the power generation region a' is connected to the lower electrode 22b of the adjacent power generation region b' is produced. (Refer to Japanese Provisional Patent Publication 48-26977.)
Another production method is described below. The lower electrodes 22a and 22b having the specified shape are formed on the substrate 21, and the amorphous semiconductor layers 23a and 23b are coated over the lower electrodes 22a and 22b. The unnecessary portions of the amorphous semiconductor layers 23a and 23b are removed by plasma etching, reverse sputtering or laser beam irradiation via a mask. Next, the upper electrodes 24a and 24b are coated over the amorphous semiconductor layers 23a and 23b. By removing the unnecessary portions of the upper electrodes 24a and 24b in the same way as described above, the conventional photovoltaic device in which the power generation regions are connected in series can also be produced. (Refer to Japanese Patent Provisional Publication 57-12568.)
When the power generation regions a' and b' of the conventional photovoltaic device described above are illuminated, electrons are generated in the amorphous semiconductor layers 23a and 23b. As a result, a potential difference is generated between the lower electrode 22a and the upper electrode 24a and between the lower electrode 22b and the upper electrode 24b.
In addition, since the upper electrode 24a of the power generation region a' is electrically connected to the lower electrode 22b, of the power generation region b', and the electromotive force of the power generation region a' is added to that of the power generation region b'.
However, it is necessary to frequently move a mask or use a plurality of masks to obtain series connections of electrodes when the conventional photovoltaic device is produced. This production method causes problems. That is, layers may be damaged when the mask is placed and removed, and improper connection may be caused due to improper operation.
In addition, since the lower electrode and upper electrode, both having a thickness of approximately 1 .mu.m, are placed one over another at the connection region, the photovoltaic device has a large series resistance when a plurality of power generation regions are connected in series. Therefore, it was difficult to obtain sufficient photovoltaic output.